1. Field of the Invention
The present invention is related to full and half duplex communication in a communications system.
2. Background Art
Simultaneous point-to-point communication between two transceivers is typically implemented with either a full duplex or a half duplex transmission scheme. Half duplex communication uses two dedicated channels connecting the transceivers. Each channel transmits data in a single direction. In full duplex communication, two transceivers use a single shared channel supporting simultaneous transmission in both directions. Full duplex communication increases the data rate by a factor of two over half duplex transmission. However, full duplex systems can require more complex circuitry and signal processing for transceivers on both ends of a single channel to transmit simultaneously.
One example communication system can be gigabit Ethernet, which is almost always full duplex. When a signal is transmitted over a wire, a part of the signal (e.g., echo, structural return loss, etc.) is reflected back, and the magnitude of the remaining portion of the signal is a function of the length of the wire. As the wire increases in length, the echo may remain the same magnitude, but a received signal becomes increasingly attenuated due to the long wires. At a certain point, a received signal having too small a magnitude can be drowned out by the echo.
In the cases where long wires are used, a substantial amount of a signal that is being processed can be the undesired echo. A more complex signal processing method has to occur to compensate for and recover the weak received signal. This is because a receiver has a limited dynamic range, which is usually used to amplify the received signal. However, with a large undesired echo the entire range can be overwhelmed by the echo.
An analog-to-digital converter (ADC) in the communications system is most significantly impacted by this situation. Typically, the ADC takes a received analog signal and turns it into a digital representation. However, when the received signal is weak, a very high number of bits are required for the ADC to operate because the system has to quantize the small signal and the large echo. This can require a complex, high power, and very expensive circuitry.
If digital echo cancellation is to be used to remove the echo from the received full duplex signal, an ADC must first quantize it. To reliably recover data from the remote transmitter, the quantization step size of the ADC must be small relative to the portion of the received signal that is due to the remote transmitter. Because of the large echo, the accuracy (e.g., number of bits, linearity, clock jitter, etc.) required from the ADC is higher in full duplex than in half duplex communication schemes. However, in many transmission channels, such as twisted pair cables, full duplex high data rates can easily require high speed ADC's with resolution requirements (e.g., number of bits) beyond what is realistically achievable in today's technology.
Therefore, what is needed is a system and method than allow for high data rates without canceling out, from a received signal, the echo from a locally transmitted signal.